The 22-year-old, who has captained England at every level up to the Under-20s, is currently on loan at Stevenage.

Knill told the club's official website: "I must have watched him 10 times. He has also played against my teams three or four times on top of that.

"He fits into what we like, he's a really good footballer, who is technically as good as anything we have got. On top of that he's 22, so he's a good age as well.

"He played in the first team at Middlesbrough at 18, but since then for a variety of reasons things haven't worked out. Now he needs to play football and we're hopeful that if things can be agreed we can give him the chance to do that."

Walker made his first-team debut at Middlesbrough in 2006 and had loan spells at Bournemouth, Aberdeen and Rotherham before joining Watford as a free signing in August 2010. He has since had two stints on loan at Stevenage and a spell at Northampton.